1. Field of the Invention
The present invention is generally related to systems and methods for diagnosis and/or treating vision in a patient. Embodiments of the invention encompass treatment techniques and systems that mitigate changes of the eye during a diagnostic and/or treatment procedure of the eye, in particular that mitigate changes in pupil size so as to allow for more accurate alignment and tracking of eye movements during a procedure. The present invention is particularly useful for enhancing the accuracy and efficacy of laser eye surgical procedures such as photorefractive keratectomy (PRK), phototherapeutic keratectomy (PTK), laser in situ keratomileusis (LASIK), and the like.
Laser eye surgical procedures benefit from precise alignment between the corneal tissues of the eye and a therapeutic laser beam. Known laser eye procedures generally employ an ultraviolet or infrared laser to remove a microscopic layer of stromal tissue from the cornea of the eye to change the cornea's contour for varying purposes, such as correcting myopia, hyperopia, astigmatism, and the like. Typically, the laser removes a selected portion of the corneal tissue to correct refractive errors of the eye. Ultraviolet laser ablation results in photodecomposition of the corneal tissue, but generally does not cause significant thermal damage to adjacent and underlying tissues of the eye. The irradiated molecules are broken into smaller volatile fragments photochemically, directly breaking the intermolecular bonds.
Laser eye surgical systems often rely on a diagnostic refractive map of the patient's cornea to determine the precise contours to ablate with the therapeutic laser. For instance, wavefront technology measures and maps ocular aberrations of the eye, typically when the pupil is relatively large. The map is then used to create an ablation pattern which includes the positions as well as the depths of the proposed corneal ablations for correcting the aberrations. Precise alignment of the corneal tissues and the therapeutic laser beam is highly beneficial for the procedure. To ensure proper alignment between the ablation pattern and the surface of the cornea, systems rely on a variety of systems and methods, including the use of moveable apertures, controlled scanning systems, eye movement tracking mechanisms, and the like. These systems are generally adapted for use while the patient is awake. To adjust for movement of the eye during a procedure, tracking systems identify and track a reference feature of the eye, which may include any a pupil, an iris feature, a boundary of the iris and the sclera, and/or the location of the pupil center. The patient can further enhance alignment between the eye and the therapeutic laser beam by focusing on a fixation target during the procedure.
While laser scanning and eye tracking technology has provided significant benefits to refractive therapies in recent years, still further improvements would be desirable. For example, along with tracking overall changes in locations of the patient's eyes (such as when a patient slightly looks away from a fixation target), more recently developed systems have sought to both register a treatment with the eye and track an orientation of the eye during laser eye surgery (particularly the torsional orientation of the eye about the optical viewing axis). While both torsional registration and tracking have been performed, development and implementation of a highly robust torsional tracking system has been found to be particularly challenging. Work in connection with the present invention has identified changes in the eye during a procedure which may play a significant role in degradation and/or loss of tracking during a procedure. Hence, improved devices, systems, and/or methods which alleviate or overcome these challenges would be beneficial.
2. Description of the Background Art
U.S. Pat. No. 4,478,449, describes an operation microscope which incorporates an eye fixation device. U.S. Pat. No. 5,549,597, describes an in situ axis alignment module for determining the astigmatic axis of a patient, and for aligning the cylindrical axis of a laser ablation system for ophthalmological surgery. U.S. Pat. No. 5,258,787, describes an ophthalmologic apparatus having an illumination optical system for directing light onto a prescribed point of an eye, and an observation optical system for observing an image of the prescribed point. U.S. Pat. No. 5,557,352, describes a method and apparatus for measuring the visual acuity and refraction of the human eye during and immediately after ocular surgery.
U.S. patent application Ser. No. 09/545,240, entitled “Two Camera Off-Axis Eye Tracker for Laser Eye Surgery” as filed on Apr. 7, 2000, now issued as U.S. Pat. No. 6,322,216, describes an off-axis eye tracker which might be modified to measure pupil center drift. U.S. patent application Ser. No. 10/300,714, entitled “Methods and Systems for Tracking a Torsional Orientation and Position of an Eye” as filed on Nov. 19, 2002, now issued as U.S. Pat. No. 7,044,602, describes a torsional tracking system which uses image registering to track a position and a torsional orientation of the patient's eye during laser eye surgery so as to align a customized ablation profile with the patient's eye.
In light of the above, it would be desirable to provide improved ophthalmological systems, devices, and methods. It would be particularly desirable to provide methods and devices which can accurately register the patient's eye and mitigate changes in the eye characteristics to allow for tracking of positional movement and torsional rotation of the patient's eye. These methods and devices would be particularly useful for use with a customized ablation pattern. Additionally, it would be desirable to mitigate changes in pupil size to allow for more accurate tracking of positional movement and torsional rotation of the patient's eyes during other diagnostic and/or treatment procedures.